1. Field of the Invention
The present invention relates to a printer, and more specifically to a rotation transmission mechanism to transmit the rotation of a drive gear on the printer body side to a driven gear as a rotation power source on a paper feeder side.
2. Description of the Prior Art
There are known printers used as output devices for computer systems, office automation and otherwise, for example it is well known that there is Japanese Utility Model Application Laid-open Print No. 62-163331.
A conventional printer will be described below with reference to FIG. 21. In the drawing, 201 is a printer which consists of a printer body 202 and a paper feeder 203, wherein the paper feeder 203 can be placed in position on the printer body 203 and also detached therefrom. This structure will be described in detail below.
Reference numeral 204 is a platen of the printer body 202. Both ends of its shaft 204a are rotatably attached to a frame 205 of the printer body 202. This shaft 204a has side plates 206a, 206b of a frame body 206 of the above paper feeder 203 detachably attached thereto, and also has a small DC motor 208 connected via a gear train 207.
On the other hand, the feeder 203 has a paper feeding shaft 209 rotatably and horizontally mounted between the right and left side plates 206a, 206b which constitute the frame 206. The paper feeding shaft 209 is provided with a paper feeding rubber roller 210.
Reference numeral 211 is a paper discharge roller which is mounted on a roller shaft 212 which is rotatably set horizontally between the right and left side plates 206a, 206b.
Rotation of the printer body 202 is transmitted to a rotation transmission shaft 216 from a drive gear 213 attached to the shaft 204a via driven gears 214 and 215 on the paper feeder 203 side. Rotation of the rotation transmission shaft 216 drives the paper feeding shaft 209 and the roller shaft 212 by gear transmission. Specifically, engaging the drive gear 213 with the driven gear 214 transmits the rotation of the printer body 202 to the paper feeder 203.
The platen shaft 204a is detachably attached with the side plates 206a, 206b of the frame body 206 of the above paper feeder 203. Thus, when the paper feeder 203 is placed in position on the printer 202, the paper feeder 203 is accurately positioned with regard to the printer body 202 so as to engage the drive gear 213 with the driven gear 214.
Such a printer has a structure that the right and left side plates 206a, 206b are directly carried by the platen shaft 204a so as to engage the drive gear 213 with the driven gear 214, so that the engagement of the drive gear 213 with the driven gear 214 based on the right and left side plates 206a, 206b is done precisely and easily.
Because the weight of the paper feeder 203 is supported by the platen shaft 204 via the both side plates 206a, 206b, however, it is required to make the platen shaft 204a and the frame 205 be tough. Also, the weight of the paper feeder 203 may degrade accurate operation of the printer 201 or induce resonance of the printer 202 and the paper feeder 203, resulting in deterioration of the appearance of letters typed on printer 201.
Therefore, the drive gear 213 and the driven gear 214 are not designed to be engaged with reference to both side plates 206a, 206b, but as shown in FIG. 22, a side cover 217 is produced to have a structure to be placed on a printer body cover 218 which forms a periphery of the top opening of the printer body 202, so that the platen shaft 204a does not have to directly support the weight of the paper feeder 203, thus remedying the above drawbacks. In this case, it becomes necessary to secure a precise engagement of the drive gear 213 with the driven gear 214 as shown in FIG. 21, but such an accurate engagement of those gears are not realized, resulting in causing an uncertain transmission of the rotation from one gear to another and breakage of gear teeth, too.
The reasons include that as shown in FIGS. 21 and 22, a reference face for placing the paper feeder 203 on the printer body 202 consists of the printer body cover 218 of the printer body 202 and the side cover 217 of the paper feeder 203. Thus it is necessary to secure precision of the drive gear 213 with respect to the printer body cover 218 and that of the driven gear 214 to the side cover 217, but because the printer body cover 218 and the side cover 217 are originally produced to provide dust prevention and noise reduction, their produced sizes are not necessarily uniform. Therefore, it is difficult to secure a precise engagement of the drive gear 213 with the driven gear 214.
And in FIGS. 21 and 22, the drive gear 213 and the driven gear 214 are required to be engaged precisely but, when the paper feeder 203 is placed on the printer body 202, the engaging operation of the driven gear 214 and the drive gear 213 and the mating operation to place in position the frame body 206 of the paper feeder 203 onto the printer body 202 are determined by their order with the engaging operation first and the mating operation next, thus placing the paper feeder 203 in position on the printer body 202 to be engaged with each other and resulting in determining the relative relation between the gears. In this case, the paper feeder 202 is not stably placed in a proper position on the printer body 202 but in loose contact with it. Therefore, the frame body 206 of the paper feeder 203 and the printer body 202 are not mated stably with each other. Thus, there are drawbacks in that transmission of the rotation between the gears is uncertain and the gear teeth may be broken.